Data received from a sensor measuring a real world physical quantity likely contains accurate measurement data as well as erroneous data. Sensors often generate erroneous data due to noise in the measurement environment or other variables affecting the sensor measurement.
One type of sensor that is prone to erroneous data outputs is an acoustic proximity sensor. Acoustic proximity sensors provide output data that relates to the distance from the sensor to an object. Acoustic proximity sensors operate by generating an acoustic pulse and measuring the time from when the acoustic pulse is sent to when a return pulse (echo) is received. When sent, the acoustic pulse propagates away from the sensor through the air, water, or other liquid medium until reaching a solid object. When the pulse hits the solid object, a return pulse is reflected back towards the sensor. The time between when the initial pulse is sent and when the return pulse is received is used to determine the distance from the sensor to the object.
Along with the return pulse, the sensor also receives multipath signals and noise. Multipath signals are caused when the acoustic pulse echoes off of surfaces other than the object to which the distance is being measured. For example, a portion of the acoustic pulse may reflect directly back to the sensor, however, other portions of the acoustic pulse may reflect off of the object in directions not directly back toward the sensor. These other reflected signals may then reflect off of other objects and return to the sensor. These signals are referred to as multipath signals. The multipath signals are detected by the sensor, but the time between when the acoustic pulse was sent and when the multipath signal(s) is received does not represent an accurate distance to the object. Thus, the data output from the sensor based on the multipath signal received is erroneous data that does not represent an accurate distance to the object. Furthermore, environmental noise may also be interpreted by the sensor as a return signal. Thus, environmental noise may also cause erroneous data to be output from the sensor. Additionally, other factors may cause erroneous data output.